(1) Field of the Invention
The present invention relates to stereo loudspeaker designs, and more particularly to columnar loudspeaker cabinets enclosing vertical arrays of speakers that produce accurate stereo sound imaging in both vertical and horizontal planes.
(2) Description of the Related Art
Systems for stereophonic sound production typically may include two sound sources, each comprising one or more speakers mounted in an enclosure. Conventionally, speaker enclosures have limited vertical height. The vertical height of the source enclosure limits the vertical height of the sound produced by the speakers of the enclosure. This, in turn, limits the vertical height of the stereo sound image produced by the two sound sources. For example, in listening to a stereo reproduction of an orchestral performance, most speakers create a realistic impression of the stage width of the live performance by horizontally spacing the reproduced sounds of different musical instruments. However, the limited vertical height of the speaker enclosures prevents an accurate recreation of the actual vertical height of the instruments on the stage during the live performance. The true benefit of the present speaker is the perceived height of the live performance spread across a soundstage of impressive height.
The cabinet enclosure construction may also be detrimental to the quality of the stereo sound image produced by the sources. Speakers are commonly mounted in the cabinet enclosures in a recessed position in the face of the cabinet, commonly called a baffle. The mounting of the speakers in the cabinet may expose portions of the cabinet structure to the path of travel of sound waves produced by the speakers. The sound waves produced by the speakers will reflect off any obstructions in their path. (See U.S. Pat. No. 4,289,929). These early reflections of the sound waves or secondary waves cause two problems. They interfere with the primary sound waves produced by the speakers, causing cancellation of some sound frequencies and exaggeration of others, so that the sound heard by the listener is not a true reproduction, but a colorized reproduction influenced by the secondary waves. Secondly, the stereo sound image is produced by sound wave time domain differences. The secondary sound waves produced by the early reflections of the primary sound waves do not have the same time domain difference of the primary sound waves. This reduces the ability of the speakers to reproduce an accurate stereo image and results in a lack of focus of the stereo sound image produced. Producing the sound waves in a correct time domain relation produces a life-like stereo image.
One type of prior art speaker arrangement is illustrated in U.S. Pat. No. 4,653,606 wherein the speakers are arranged both vertically and horizontally. However, this arrangement does not take into account the vertical placement of various sounds and is lacking in the height quality obtained by the present invention. Also the line source speakers of this type are lacking in the bass region. The arrangement obtains a prescribed directional response pattern by operating each of the different driver elements individually through specific frequency ranges, and all of the drivers are not operated through the full range of frequencies.
The present invention obtains vertical height reproduction of all instruments. It operates as a true line source through all frequencies of the music, by emitting sound through all frequencies, top to bottom.
Another type of speaker employed heretofore had individual drivers staggered at varying depths in relation to their voice coil position, and also a prior art baffleless design. This could be illustrated by the Dalquist speakers. This type of speaker, with minimum baffles, did eliminate baffle related problems such as the early reflections from the baffles of secondary waves that interfere with the primary waves causing cancellation of some frequencies and exaggeration of others, and the reflections from the baffles of secondary waves that are not in the same time domain as the primary waves, causing a lack of focus and a slight phase shift of the stereo image. This type of speaker arrangement had an extremely narrow sweet spot, little vertical height, very low efficiency and low bass output.
A type of speaker system that is similar to the Dalquist design is disclosed in U.S. Pat. No. 4,289,929. This type of speaker design also eliminated the baffle related problem of secondary or standing sound waves that resulted in "phantom drivers" producing sound other than what comes from the driver itself. However, this design provided only a single driver in a baffleless situation and was not a true line source.
Other prior art speaker systems include long vertical columns of tweeters with separate relatively low mountings of bass or woofer speakers. This is illustrated by the McIntosh speaker, with 23 tweeter elements mounted in a manner to provide a baffle arrangement with a consequent distortion. Although this design provides an improvement in vertical height over other designs, it still uses a baffle surrounding the tweeter arrays, has unimpressive vertical height, and the high frequency range of the speaker is the only part of the music reproduced as a line source configuration.
The present invention seeks to overcome these shortcomings of conventional loudspeaker systems.
It is therefore an object of the present invention to provide an improved loudspeaker system that produces a stereo sound image in both a horizontal plane and an extended vertical plane, while avoiding a reduction in the quality of the stereo sound image produced due to early reflections of sound waves.